A student-prepared silver−silver chloride reference electrode is described. The chemical deposition of AgCl(s) onto Ag(s) is accomplished in 30−50 s by placement of a Ag(s) wire in laundry bleach. An autopipettor tip with an agarose gel plug serves as the electrode housing; the agarose gel contains predissolved KNO 3 . Reference electrode preparation is completed in about 10 min, allowing enough time for laboratory exercises that utilize the electrode. Preparation and operation of the electrode and recovery of the Ag(s) are designed to teach a number of important chemistry principles.

The catalyzed H 2 O 2 decomposition reaction is 2H 2 O 2 ðaqÞ sf catalyst 2H 2 OðlÞ þ O 2 ðgÞ (1Þ A procedure to determine the kinetics of the iodide-catalyzed H 2 O 2 decomposition reaction based on water displacement from a wash bottle has been reported by Teggins and Mahaffy (1). In this procedure, the H 2 O 2 and KI reagents totaling 300 mL are mixed and transferred to a wash bottle. As O 2 (g) is generated, some of the reaction solution is displaced. The initial rate of reaction is determined by measuring the time to displace specific volumes. By comparing the initial rates for different runs, the orders of reaction were both found to be 1. Compared to conventional water displacement schemes (2, 3), this approach is attractive because it is easily performed. We have reported a wash bottle water displacement scheme to determine the % NaHCO 3 in an Alka-Seltzer tablet, the molar mass of CO 2 , and the ideal gas constant R (4). Encouraged by the quality of results obtained by students, we have examined the Teggins and Mahaffy (1) wash bottle water displacement scheme and found the following changes to be helpful: (i) Reagents are added to a test tube placed in a water-filled wash bottle so that water is displaced instead of the reaction H 2 O 2 -KI solution. (ii) Small volumes of reagents totaling 5 mL are used. Theory Initial Rate Measurement Based on Volume of O 2 (g)The initial rate is defined asis the volume of the reaction solution in liters (L), and Δt is the displaced water collection time in seconds (s). Considering the equationwhere k is the rate constant, h is the order with respect to H 2 O 2 , and i is the order with respect to I -, the rate constant will have units ofIt is essential to include V(solution) in the definition of initial rate in eq 2 so that the rate constant in eq 4 is applicable to any volume of reaction solution. Initial Rate Measurement Based on Concentration of H 2 O 2Based on H 2 O 2 concentration, the initial rate isThe temperature of the gas in the wash bottle and the room atmospheric pressure (P(atm) = P(O 2 (g)) are measured so that the V(O 2 (g)) can be converted to mol O 2 (g) according to the ideal gas law. Considering the equation initial rate -Δ½H 2 O 2 2Δt ¼ k½H 2 O 2 h ½I -i (7Þ the rate constant will have units of rate constant units ¼ M ð1 -h -iÞ s -1 (8Þ The rate constant for the H 2 O 2 decomposition is conventionally expressed according to eq 8. Order of Reaction with Respect to H 2 O 2 With [I -] fixed and the [H 2 O 2 ] varied from one run to another initial rate ¼ -Δ½H 2 O 2 2Δt ¼ k½I -i ½H 2 O 2 h ¼ k 0 ½H 2 O 2 h (9Þ where k 0 ¼ k½I -i (10Þ The order of the reaction with respect to [H 2 O 2 ] can be

The acid ionization constant, K a , of acetic acid and the base ionization constant, K b , of ammonia are determined easily and rapidly using a datalogger, a pH sensor, and a conductivity sensor. To decrease sample preparation time and to minimize waste, sequential aliquots of a concentrated standard are added to a known volume of water and measurements are made after each addition. In this laboratory exercise, students show that K a and K b are constants, compare and contrast pH and conductivity approaches, and evaluate how solution components (weak acid alone and weak acid plus conjugate base) affect the results.

Using a conductivity sensor, a temperature sensor, and a datalogger, fundamental factors that affect conductivity are explored. These factors are (i) concentration, (ii) temperature, (iii) ion charge, and (iv) size and or mass of anion. In addition, the conductivities of a number of other solutions are measured. This lab has been designed to provide students opportunities to construct knowledge.

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